Unit D Chapter 1 Lesson 1 Pages D6-D11 Earth’s Structure Unit D Chapter 1 Lesson 1 Pages D6-D11

Earth’s Layers Our planet is about 4.54 billion years old (give or take a few million) It started out as a huge collection of molten rock which formed our planet. As the outer layer started to cool (it took about 400million years) it formed our crust. Artist conception of early Earth….not quite ready for life.

Earth’s Layers You would have to travel about 4000 miles to reach the center of the planet. Unfortunately, you would be completely destroyed by doing this. Temperatures near the center are over 10,000 degrees F. The pressure is also so extreme it would smash you into people paste. Hollywood lies to us once again!!! Curse you Brendan Fraser!! Next thing you know, we’ll find out mummies don’t come back from the dead either.

Earth’s Layers How do we know information on the inner layers if we can’t go there? Scientists can drill down for the first 6 miles or so in the crust. They must base their hypotheses on the patterns and speed of earthquake waves and how they travel.

Earth’s Layers Earth is made of three main layers. The crust, mantle, and core. The mantle and crust have two small layers inside them called the lithosphere and asthenosphere. The core is divided into the outer and inner core.

The Crust This is what not to do when cracks in the crust open up. The crust is about 20 miles thick under the continents, and about 5 miles thick under the ocean. The continental crust is made of granite, oceanic crust is basalt, a much denser rock. Scientists are currently working on a $1billion project to drill through the oceanic crust. He learned that lesson after stepping in this.

The Lithosphere The lithosphere includes all of the crust and part of the upper mantle. It contains earth’s tectonic plates. It is divided into seven major tectonic plates. The lithosphere actually floats on top of the asthenosphere. This scuba diver is between two of the tectonic plates. He has one hand on North America, and one on Europe.

The Asthenosphere The asthenosphere is a zone of partially melted rock in the upper mantle. It has a property called plasticity, which means that it can flow. The asthenosphere flows because heat from deeper in the earth causes currents. Silly putty behaves in a similar (and safer) manner.

The Mantle The mantle is our thickest layer, about 1800 miles thick. The upper mantle is about 2900 degrees and about 7200 degrees near the core. This is hot enough to melt rock, but only the upper mantle is partially melted. The rest is solid because of tremendous pressure. Molten rock called magma can be pushed up from the mantle, escaping through cracks in the crust.

The Outer and Inner Core The outer core is an extremely hot layer of liquid metals, mostly iron and nickel. Temps range from 8-11 thousand degrees. The inner core is mostly iron and solid, with temperatures from 9-13 thousand degrees. The metals should melt at this temp, but the pressure is so great it forces it into a solid state.

Earth’s Plates Plate Tectonics is the theory scientists use to explain plate movement. Teconics comes from the Greek word meaning “builder.” The seven major plates are named for the continents or oceans they carry. The largest plate is the “Pacific Plate.” It covers 1/5 of Earth’s surface. A map of the plates can be found on page D8-D9 of your book.

Earth’s Plates The plates of the lithosphere constantly change in shape and size. They may split or combine with other plates. They can be pushed back into the earth and be melted down again. The crust under the ocean is newer, thinner crust. Continental crust is older and thicker.

Changes to Earth’s Surface Plate movement causes earth’s surface to change constantly. They form mountains, and trenches. The boundaries where plates meet are the sites of earthquakes and volcanoes. Other forces can slowly change the surface of earth. Erosion and glaciers carve away at the crust.

Changes to Earth’s Surface Earth’s surface is changed rapidly when hit by objects from space. Meteoroids are rocks floating in space, when they enter our atmosphere, they heat up and burn. They are seen as “shooting stars” but are now called meteors.

Changes to Earth’s Surface Meteors that actually hit the earth are called meteorites. More than 19,000 fall to earth each year but are so small no one notices. A few though, can make a lasting impact.